Telephone installation



Filed June 26, 1937 2 Sheets-SheetI l /N VE/vfoe Ma 752212 HeZzeZ y L TTwe/vm Oct. 24, 1939. M. HEBEL I TELEPHONE INSTALLATION Filed June 26, 1937 2 Sheets-Sheet 2 ...JL www www@ VVENTOR Mdm/z Hebel ATTORNEYS Patented Oct. 24, 1,939A

PATENT OFFICE 2,177,608 TELEPHONE INSTALLATION Martin Hebel, Hechcndorf-on-the-Iilsensee, lUpper Bavaria, Germany Application June 26, 1937, Serial No. 150,593 In Germany June 26, 1936 15v Claims.

This invention relates to telephone systems comprising a plurality v`'oi exchanges connected together by inductively coupled lines.

In such systems, it is usual for control current M. impulses to be transmitted over the speech lines of lthe exchanges in the form of direct vcurrent impulses and over the trunk lines in the form of alternatingv current` impulses. Signal current impulses which indicate to the calling subscriber 10. whether a. line is idle or busy are sent over the speech lines and'. the trunk'line' to which they are connected.` The trunk line and the speech,

lines are therefore normally connected together and are only disconnectedffor the transmission of control impulses. Rejector circuits or bridge arrangements have, therefore, to be provided in the speech lines so as to prevent the transmission over the speech lines of the A. C. control impulses while allowing the rtransmission of signal and k no speech currents. Where amplifiers are provided, special balancing devices have to be provided to prevent their self-oscillation as they tend to'howl if connected'fto the lines beiore the connection to the called subscriber is completed. One object of the invention is to provide a telephone system in which the trunk lines are normally disconnected from the speech lines in the repeatersat their two ends.

Another object'of the invention is to provide a telephone system in which a trunk line is connected to the speech lines by the action of automatic switch meanswhen the called subscriber repliesand in which the said connection is maintained only so longv as the conditions ink which conversation can take place persist. n

Other'objects of the invention will be made apparent inthe following description made with reference to the 'accompanying drawings, in which: l

40 Figure 1 shows by way oi example the essential circuits of a repeater at the outgoing end of a trunk line, and

, lFigure 2 shows the essential circuits of a repeater at the incoming end of the same line. 5k In the arrangement illustrated in the drawings, the talking circuit remains open in the repeaters until kthe called subscriber replies and is opened when one of' the subscribers hangs up his receiver. Any switch'means responsive to cur- 50 rents of audible frequency in the repeaters cannot therefore be'inuenced by the direct action of speech currents during the making of a connection. One source of wrong connections in automatic systems is thus eliminated. Ii speech 55 amplifiers are used, they are only put into the circuit when the connection has been completed so that no special balancing arrangements are needed to guard against selfoscillation and howling of the amplifiers.

In order that signalsy may be transmitted to the calling subscriber while a connection is being set up, signal transmitters are `provided on the calling side of the repeaters in the calling sub scribers exchange and are arranged so as to be controlled from the various selectors by impulses 10 transmitted backwards over the trunk line.

TheA details of the various circuits required in such an arrangement will now be' described together with an explanation of the operation of the system in the makingy of various diierent 15 kinds of calls.

I. Trunk seized for an ordinary call If the repeater Uel (Figure 1) is seized by a selector (not shown) the circuit is closed through the winding I of the relay A and the winding II of the relay C. Both relays respond. The relay A through its contacts ai and a2 connects a source of alternating current to the line VL. An alternating current impulse is thus transmitted 25 through the inductively connected repeater and the trunk line VL. The'duration of this current impulse which is emitted automatically when the line is seized is limited by the response of the relay C, the contactv cl of which short circuits the winding I of the relay A. When the relay A drops, a slow-to-respond relay Q is energised over'the contacts c1' and a5 and, by means of its contact q2, switches in the slow-to-respond relay U. The contact a4 then short circuits the 35 relay Q. During the brief response oi the relay Q, the winding I of the relay F, which is earthed, is connected bymeans of the Contact ql to one wire of the speech line until reversal of the contact u2 so as to receive the characteristic signal of the toll exchange which is given by causing current to flow through the wire in question when the toll exchange seizes the repeater.

If the rst selecting current impulse arrives too early,` i. e. before the relay Q has dropped, the relay Bes is energised in the circuit:

-l, a-Wire of the incoming line contacts g2, bl, winding II of relay A, contacts ql, u2, `winding I of relay Bes,

A holding circuit is closed for the winding II of the relay Bes over the contacts c2 and bes2. Thel contact besl causes current to flow over the resistance Wz'2 and the b-wire of the incoming line. This causes the connection to beunmade in a selector nearer the calling subscriber. A 55 busy signal can be transmitted to the caller over the calling line.

The relay J in the repeater Ue2 (Figure 2) is energised by the short current impulse received by a signal receiver Vll which is tuned to audible frequency. Thev contact :il energises a relay AR- and the contact ar5 switches in the relay CR and, after the Contact cr3 has opened, the relay E. The contact cr5 closes a holding circuit for the relays CR and E; the contact er? earths the wire BL to the next selector,fgroup selector or nal selector LW. vAt the end of thecurrent impulse, the relay AR drops. The slowacting relay f QR is now energised over the contacts 'cr|, art

and nr4, and by means of its contactqrZ switches l in the slow acting relay. UR. 'The relay UR, by means of its contact url-l, opens the circuitfor-the relay QR so that the latter drops.

upon the contact ar3. After its energisation, the relay UR opens the circuit for the relayy QR at the contact urli and the circuit for the relay FR at the Contact ur3. The relays QR and therefore drop. l

II. Trunk seized ,for a toll call When the repeater Uel (Figure 1) is seized by a trunk exchange the operations described above first of all take place. rThe relay F (Figure 1) is then, however, also energised because its wind ing I is connected to thea-wire for a short time over the contacts bl,'ql and n2', as the seizing is accompanied by a flow of current through the a-wire. The following circuit is made:

winding I of relay F, contacts u2, ql, winding II of relay A, contacts bl, g2, a-wire The relays A and F respond inthis circuit. The v contact ffl closes a holding circuit for the winding II of the relay F over the contact c2. The relay A necessarily transmits a further seizing current impulse to the line VL over the contacts al and a2, the duration of this impulse being limited by the response of the relay U.

This second seizing `current impulse energises the relay FR in the repeater Ue2 (Figure 2) over the Contact ar3, the circuit being prepared by the contact qr3 until yenergization of the'relay UR. A holding circuit is 'closed for the relay FR over the contacts crl and fr2. The contact frsl causes current to flow through the choke coil Drol and the contacts frd, trl, qrl, tr3, to the upperwire of the line leading to the next selector. A relay FA in this selector is thus energised so that the selector is set for toll connections.

' v III. Transmission of impulses If the calling subscriber or the trunk toll exchange begins with the numerical selection for setting the group selectors and the Vinal selector on to the desired subscribers line, the awire .of the` speech line in the groupselector (not shown) is earthed at each current impulse. The

connects at the contact bl the winding II of the relay A from the a-wire for the remainder of the incoming current impulses and connects the Wind,-

The contactA `'qr3 switches the relay FR into a circuit dependent ing III of the relay B to this a-wire in place of the winding II of the relay A. The relay Ais thus energised only for a short time even when long current impulses are received. The source of alternating current is connected to 'thespeech wire by the contacts al and a2 at eachrenergisation. The current impulses are thus transmitted over the line VL to the signal receiver V4 of the repeater -Ue2 (Figure 2) and thus to the relay J. The relay J responds at each current impulse and energises the relay AR. The contact ar3 energises the relay VR, the release of which is delayed until after the reception of a current impulse contacts url, arl, qrl, tr3, upper wire of the line to the group or final selector.

In 'the case of long distance traffic, when the relays F (Figure 1) and FR (Figure 2) are energised, current is suppliedy to this Wire over the choke coil Drol and the contacts fr4, tr4, 0T2, arl, trS before and after each train of current impulses.

IV. AZZ Zines of the group selector or the desired subscribers Zine are busy in the iinal selector LW by the Contact nal kwhich is opened during the setting of the nal selector:

resistance Wild, contacts ual, pal, lower wire of the speech line, relay MR, contacts el, lr3, winding II of the relay K, contact 'tr-8, -l.

The resistance Willi is so designed that in both cases only the relay MR and not the relay K responds. The contact mrl short circuits the slow acting relay which is energised when the repeaterv is seized by the contact cr'l. The contact mrg energises the relay SR in the circuit:

-{, contacts cr, kil, nrl, mrZ, winding II of the relay SR,

By means of its contacts srl, sr2, therelay SR connects the source of alternating current, to fthe line VL. The flow of alternating'current is stopped after approximately 400 millisecondsby the dropping of the slow acting relay NR, the contact nrl of which opens the circuit for the relay SR.

In the repeater Uel (Figure 1) this long alternating current impulse is received by the signal receiver Vl. The relay W is energised so that its contact wi energises a vrelay H, the Contact h2 of which energises `a relay Y. The contact y2 of thelatter relay causes current to flow over the resistance Wil-2 andthe contacts il, azi, y2, g3, to the bwire of the incoming speech line. This causes the connection to be unmade at one of the selectors. A busy signal can be transmitted to the calling subscriber.

V. Release of the connection before conversation If, for example, the circuit through the celine y lay Ais energised in a circuit running overv the contacts c4, nB, gS, and the `rest contact and wiper b of a transmitting switch SS so thatthe source of alternating current is connected to the i line` by the contacts al and a2. Alternating current thus flows for the duration of the delay in release of the relay U. The holding circuits for thevarious relays of therepeater Uel are opened on release of the relay C so thatfthese relays drop. On the other hand, the contact a4 causes the slow acting relay V to be energised so that the contact UI opens the circuit through the c-wre and thus prevents `further seizing of the repeater Uel. When the relay U releases, the relay A is de-energised as, consequently, is the relay V. The repeater Uel can then be seized again. The long alternating current impulse is received in the repeater'UeZ (Figure 2)by the signal receiver V4. The relay J is energised and its contact il switches in the relay AR. The latter short-circuits the relay CR over the contacts 6W5, e2, tri), which drops only upon reception -oi this long current impulse. Release of the relay CR causes the circuits of the various relays of the repeater Ue2 to be interrupted. The circuit for the line BL is also opened at the contact GT2 so as to cause the following selectors to be released.

VI. Desired subscriber is free If, however, the desired subscriber is free, the calling subscriber or the trunk exchange must receive the free or idle signal. Since the speech line is interrupted at the contacts g2 and g3 in the repeater Uel and at the contact tr3 in the rewire` ofthe speech line, relay MR, contacts el,

lf3, winding II of relay K, contact 151'8,

The resistance Willi is so designed that in this circuit only the relay MR responds and not the k relay K. The relay MR energises the relay SR to the line VL by the contacts srl and ST2. The

length of the short alternating current impulse thus `transmitted is limited by the release of the slow acting relay UA in the nal selector LW, the circuit of which is interrupted in known manner when the final selector has been set.

The relay W in the repeater Uel (Figure 1) is energised by the short impulse received by the current receiver VI. Its contact wl energises the relay I-I and its contact h2 energises the relay Y so that the contact y2 causes current to flow over the resistance Wz'Z and the contacts tl xl, y2, g3 to the b-wire of the incoming line. At the end of the received current impulse, the relay W drops so that the relay I-I is cie-energised and the relay K energised in the circuit:

. contacts c3, o9, h2, 314, winding I of relay X,

relay Y,

The contact :ci now earths the b-wire of the incoming line. A free signal is thus sent to the calling subscriber Irornthe selectory onAv the calling VII. Response of the called subscriber in an ordinary call If his line is free, the wanted subscriber is called automatically in the usual way if the connectlon has been made by an ordinary subscriber. When the called subscriber removes his receiver, the relay YA of the final selector LW (Figure 2) responds and energises a relay ZA which responds 60 milliseconds later and throws its contact zal. Thefollowing circuit remains closed during the 60 milliseconds delay in response of the relay ZA:

resistance Wi! 5, contacts zal, yal, no2, pal, lower wire of the speech line, relay MR, contacts el, Zr3, winding II of relay K, contact tra,

The relays MR and K are `energised in this circuit. Contact kd prevents the winding II of the relay SR from being affected by the contact m12. The contact kl closes a circuit for the slow-torespond relay LR which responds afteran interval of 80 milliseconds. Until the response of the relay LR, the relay SR is energised over the contacts trl l, k2, lf2. The contacts srl, ST2 send alternating current to the line. When the relay LR responds, the contact ZTI switches in the relay TR. Consequently, the contact tr closes a holding circuit for its relay TR; the contact trB disconnects the winding II of the relay K and the relay MR; the contact tr5 interrupts the circuit for the winding I of the relay K and for the relay LR; the contact trl l interrupts the circuit for the winding I of the relay SR so that this relay cannot be energised when the relays K and LR drop successively on opening of the contact zal; the contact t1'3 switches in the speech line; the contacts trl and t12 remove the short circuit for the speech amplifier V3; the contact fr!) opens so that the short circuit for the relay CR is controlled by the contact 1182 of a double armature relay RR which, as will be described below, can be energised only un receipt of a certain current impulse combinaion.

In the outgoing repeater Uel (Figure l) a current impulse having a duration of 8D milliseconds is received by the relay W which energises the relay H. The contact h2 interrupts the circuit for relay Y and closes a circuit through the winding II of the relay X. At the end of the current impulse, this circuit is interrupted at the contact h2 and the relay X drops.

'Ihe relay G is now energised in the circuit:

+, contacts c2, t2, rsi, r2, relay G,

The 'contacts g2 and g3 switch in the speech line. The contacts gill and gli remove the short circuit for the amplifier V2. The contact gli prevents the relay I-I, and the contact g5) the relays X and Y from being switched in again. The contact 96 prepares the energisation of the relay L and the contact g'l the energisation of the relays O, P and R.

VIII. Response of the called subscriber in a roll connection If the connection has been made by a toll operator, the relays F (Figure 1) FR (Figure 2) and the nal selector relay FA are energised. When the called subscriber replies, current is caused to ow continuously to the b-wire of the speech line over the closed Contact fa! independently of the contact/zal. In the repeater UeZ, the relays K, LR and TR are also energised in the manner described and an alternating current impulse of 80 milliseconds duration is sent back through the line. The relay G in the repeater Uel is thereby energised in the manner described and switches in the speech line. Also, current is causedrto flow to the b-wire of the incoming line over the choke coil Dro and the contacts fl, gl, so that a signal is given to the operator in the toll exchange.

IX. Cutting 017 in an ordinary connectionl Owing to the speech lines being switched in at the contacts g2, g3, in the repeater Uel, when the called subscriber replies, the signal receivers Vl and Vfl which are tuned to audible frequency and thus the receiving relays W (Figure l) and JA (Figure 2) are acted upon by the speech currents. These may cause the relays to be operated in an unforeseen manner and it is necessary to provide against the possibility 'of the speech transmission being thereby interrupted or other undesired operations such as cutting voff of the connection occurring. On the other hand, it must still be possible to cut off the connection when one of the;

calling subscriber replaces his receiver, the relayl C (Figure l) drops and the contact c1 opens the circuit of the slow-acting relayU. As the relay G was energised at the beginning of the conversation, the following circuit for the relays L, S is now closed until the relay U releases:

contact s2, relay S, contacts c4, c6, a6

rest position and wiper a of the transmitting switch SS, contact d, relay L, .A

The relay S is connected in a holding circuit by the contacts s2 and h3. The contact ll switches in the stepping magnet D of the transmitting switch SS; the contact 8| interrupts the circuit through the c-wire of the incoming line and thereby prevents the repeater Uel from being seized again; the contact c2 disconnects the slowto-release relay G and the relay `T. The speech line is thus interrupted and the receiving relays are removed from the influenceof the calling subscribers speech currents. The relay L and the magnet D of the transmitting switch SS -operate alternately. The magnet D is therefore energised intermittently and steps the wipers a, b of the transmitter switch SS. The first step brings the wiper b on to an earthed contact. The

winding III of the relay A remains energised for 50 milliseconds. When the wiper comes on to the second contact, the relay A is disconnected from earth for 50 milliseconds and releases. By connecting a number of successive contactsito earth, the relay A can be held energised for correspondingly longer periods, for example 300 milliseconds; The energisation of the relay A and, therefore, the emission of alternating current bythe contacts al and a2 over the line VL are thus controlled by the wiring of the contact bank wiped overby thewiper b. Let us assume that the current impulse combination is sent out. The relay J in the repeater U62 responds rhythmically with the current impulses received by the signal receiver V4. The contact :il energises the relay AR and the contact ar3 switches in the relay VR which, being slow-acting, remains energised for the duration of receipt of the current impulse combination; The contact arl controls a device comprising the two-stepvrelays OR, PR, RR and WR.A The contacts ofthese relays which are actuated at the Viirst step are marked in the drawings. After receipt of the rst current impulse, the relay OR is energised and makes its first step in the circuit: l'

windingl of relay OR, contacts arl, ur5, w3, trliLnrZ, rrs, yrl, crd,

On receipt of the second current impulse, the relay ORv` makes its second stepand during the pausefollowing the receipt of the second current impulse, the relay PR makes its rst step. On receipt of the third current impulse, the relay PRv makes its second step and during the pause following the receipt of the third impulse, the relay RR makes its iirst step. On receipt of the last (fourth) current impulse, the relay RR makes its second step.' When making its second step, each of the relays OR, PR and RR throws its contact os, prs, or W and is locked in a circuit which runs through the contacts m5, w3, trlll, m2, m2, `'JM and crd. The relay VR is a supervisory relay, the function of which is to determine whether the current impulses arrive at the correct time intervals. If no further current impulse is received milliseconds after the reception of an impulse, the relay VR drops and interrupts the locking circuit for the relays OR, PR and RR at its contact w3. The supervisory relay NR checks the length of the rst current impulse. Ii it* lasts longer than 100 milliseconds, the relay NR drops and opens its contact m2. On reception of a' rstcurrent impulse of the prescribed length, the relay NR is held energised by the contact ofrlZ. The exact length of the second current impulse is supervised by the relay UR which, o'n receipt of this current impulse, is short circuited by the contacts pril, and orsi. If a current impulse lasting more than 100 milliseconds is received, the relay vUR drops and opens its contact'ur. 'Ihe'length of the third current impulse is supervised by a relay XR which has a release delay of 200 milliseconds. This relay XR is short circuited by the contact m86 on receipt of the third current impulse which lasts 300 milliseconds. It is only when the relay XR drops and closes its contact rZ that the-locking circuit for the relays OR,'-PR and RR is not interrupted on receipt of the fourth current impulse. The duration of the fourth current impulse is supervised by the relays CR and YR. On receipt of the fourth current impulse which lasts 300 millisec` onds, the vrelay YR is short circuited by the contact rrs'l. The relay YR has a release delay of 200 milliseconds. If the current impulse is so short that it does not drop, further current impulses are at once received and the relay WR- is energised and makes its two steps and by means of the contact wrs interrupts the locking circuit for the relays OR, PR and RR. On receipt of the fourth current impulse,.the relay CR is short circuited by the contact w32 and drops provided the current impulse has the prescribed length of 300 milliseconds. As the relay RR can only loe energised on receipt of the fourth current impulse if the preceding short and long current impulses have been received in the right sequence, the release takes place only if the length of the received current impulse combination corresponds exactly'to' the prescribed lengths of tion has been received, the relay CR in the repeater Ue2 is released by the fourth current impulse. The relays UR, TR, NR and E* are thus deprived of current. The contact c12 interrupts the circuit through the line BL and thus brings about the release of the succeeding selector LW (Figure 2). The line VLmust be prevented from being seized again until this selector has been restored to the normal position. By means of the `Contact 1c of the selector LW which is open only in the normal `position of the selector, the iollowing circuit is close-dz.

resistance Will, contacts lc, el, lf3, winding II ofrelay K, contact tr8,

The relay K responds and, by means of its contact k2, energises the winding I of the relay SR so that the source of alternating current is connected to the line. The slow-to-attract relay LR is switched in by the contact kl and responds 80 milliseconds later and, by means of its contact lf2, interruptsthe circuit for the relay SR. The alternating current impulse Aof 80 milliseconds duration which is emitted by therelay SR is received in the repeater Uel (Figure 1) by the relay W provided that the relay V which has been energised during the emission of the current impulse combination has not yet dropped and by means of its contact vl holds the seizing circuit through th-e c-wire of the incoming line open. The relay W energises the relay I-I through its contact wl and the latter relay through its contact h2 switches in the relay Y. Upon receipt of the short current impulse, .the relay Y is locked in a circuit closed at its contact g4. lThe relay Y, by means of its contact yl, interrupts the circuit throught the c-wire even after the relay V has released. At the same time, the opening of the contact h3 deprives the relay S of current. When the selector LW returns to the normal position, the circuit for the relay K is interrupted by the contact lc. The relay SR is again switched in for the duration of the delay in release of the relay LR by the contacts trl I, k2, lf2. 'Ihe contacts srl and s1-2 again connect the source of alternating current to the line for the emission of a short current impulse. This current impulse energises the relays W and I-I in the repeater Ucl The circuit for the relays X andy Y is interrupted by the contact h2. The relay Y drops and, by means of its contact yl, preparatorily closes the seizing circuit through the `c-wire of the incoming line. The repeater Uel lcan now again be seized.

(2) -If the correct current impulse combination is not received, for example, because the called subscriber has spoken in the meantime and has operated the relay W byv means of the alternating speech currents, the relay CR in the repeater Ue2 remains energised and the short alternating current impulse is not emitted. The relay S in the repeater Uel also remains energised. The relay L is switched in by the contacts s3, v4 and the wiper a of the transmitting switch SS which, in the meantime, has returned to its normal position, and this relay, together with the magnet D inthe manner described, again steps the transmitting switch SS. A new current impulse combination is thus emitted. This procedure is repeated until the relay S has been caused to drop by the backwardly transmitted alternating current impulse. An alarm signal can be sent over the contact S5 andthe line AL if the relay S remains energised for an excessively long time.

It may be desirable in many cases not to release the connecting devices immediately the calling subscriber replaces his receiver, for example, if at the end of the conversation, current impulses are to be transmitted from the called subscribers exchange to the calling subscribers exchange which characterise the zone value of the connection from which the charge is to be calculated. In such cases, when the calling subscriber replaces his receiver, the circuit is not interrupted by'way of the c-wire of the incoming line but a circuit is closed through the a-wire of this line by which a relay RA in the repeater Ue! is energised so that the relay G deenergizes and switches in the transmitting switch for the emission of a lspecial current impulse combination.

This current impulse does not then bring about the de-energisation of the relay CR in the rep-eater Ue2, (Figure 2), but de-energises the relay TR which interrupts the speech line. In this way, the speech line is restored to the condition which exists during the setting. The relays W and J can no longer be influenced by speech currents and any desired switching operations may be transmitted rin both directions over the line. The release is effected later as described under thev foregoing sub-heading V. f

X. Clearing by the called subscriber When` a` called subscriber who has been connected by the toll exchange replaces his receiver, the relay YA of the final selector LW (Figure 2) releases again and by means of its contact ya! opens the circuit for the relay K. The relay LR 1s switched out by the contact Ici and does not drop until 80 milliseconds later. The relay BR is energisedv in the circuit:

contacts trl3, 1c5, Zr4, normal position and wiperl b of the transmitter switch SSR, contact dr, relay BR,

The contact brl switches in the stepping magnetDr ofthe transmitting switch SSR. When the relay LR releases, the contact Zr interrupts the circuit for the relay TR which again interruptsy the speech line. The relay BR and the rotary magnet Dr of the transmitter switch SSR operate alternately so that the wipers a and b are stepped on. The winding II of the relay SR connected to `the wiper a of the transmitter switch SSR is energised each time the wiper encounters an earthed contact and by means of the contacts. srl and sr2 transmits an alternating current impulse to the line VL. The current im pulse combination is thus, for example, sent out.

The relay W in the repeater Uel (Figure 1) respondsl rhythmicallyv with the received current impulse combination; The contact wl energises the relay. H in a circuit running through the contact f3 and the contact hl energises the relay yV which does not drop unless no current impulses are received over a considerable period vof time. The contact h4 controls a device comprising the two-step .relays O, P and R. The contacts of these relays which are actuated at the first step are marked i in the drawings. In the pause after the receipt of the rst current impulse, the relay O makes its rst step in the circuit:

winding l of relay O, contacts osl, h4, m2, v5, pif, ps6, 91.4--

On receipt of the second current impulse, the relay O makes its second step and during the second pause, the relay P makes its first step. 'I'he relays O, P and R are thus successively energised and are each locked in a circuit closed at the second step. The contact rsi interrupts the circuit for the relay G. The correct length of the pause between the various current impulses is supervised by the relay V which has a delayed release of milliseconds. The contact `v5 interrupts the circuit for the relays O, -P and R. The length of the rst current impulse is supervised by theV relay M which, on receipt of this impulse, is short circuited by the contacts h5, g8 and drops after 200 milliseconds.A The length of the second current impulse is supervised by the relay N which is short circuited on receipt of this impulse by the contacts h5, os8 and drops after 200 milliseconds. The length of the third current impulse is supervised by the relay M which is energised again by the contact os'l after receipt of the rst current impulse. If the third current impulse is too long, the relay M drops and its contact m3 interrupts the circuit for the relays O, P and R. The duration of the last current impulse is supervised by relays G and M. The relay G is de-energised only if thelength of the received current impulse combinationcorresponds exactly to the correct duration of the various current impulses and pauses. The contacts g2 and g3 interrupt the speechwline and thus destroy the conversation conditions in the repeater Uel. The contact gl disconnects the b-wire of the incoming line from the source of current. In this way, a signal is given in the trunk exchange which indicates that the called subscriber has replaced his receiver. The trunk exchange operator can now send out a current impulse which is transmitted over the line VL as a setting current impulse and which iniiuences means provided in the final selector for switching in a device for transmitting ringing current periodically to the desired subscriber.

If, for any reason, the called 'subscriber again removes his receiver, the speech line is again switched through as at the beginning of the conversation.

XI. Connection of the toll loperator to anengaged subscriber If the desired subscribers line has been seized from the toll exchange, the operator, by emitting through the v(JL-wire of the line a current impulse which is transmitted over the line VL as a setting current impulse, can cause the nal selector LW (Figure 2) to be connected to the engaged subscribers line. The speech lines in the repeaters Uel, Ue2 are'then switched in as at the beginning of a conversation.

XII.l Seoerzng of a local connection by the toll operator If the toll operator now wishes to sever the existing connection to the desired subscriber', she sends a fresh current impulse through the a-wire of the incoming line (Figure 1). 'I'his current impulse is received by the winding II of the relay A which is connected to the a-wire by way of the contacts f2 and g2. A current lmpulse is sent out by the contacts al and a2. At the same time, the relay L is energised by the contacts a6, f5, gli and switches in the current impulse combination transmitter switch SS, so that the current impulse combination is emitted by the periodical energisation of the winding III of the relay A. The energisation of the winding II of the relay A which causes the switching in of the impulse combination transmitter does not disturb the correct emission of the impulse combination; the iirst impulse is somewhat lengthened, but only to such an extent that the relays OR, PR, RR of Ythe repeater Ue2 (Figure 2) can still correctly respond to the received impulse combination as described above. The relay RR in the repeaterv Ue2 is again energised in the second stage on receipt of this current impulse combination. Since, however, relay FR is energised when a connection is made by the toll exchange, it is not the relay CR but the relay TR which is now short circuited andfcut out. When the relay TR releases, a current impulse is transmitted by the contacts url, arl, ql, t13 to the final selector LW and causes the existing connection to be interrupted therein. The .relay YA then responds again sothat the relays K and LR are energised. The contact Irl switches in the relay TR so that the speech lines in the repeater UeZ are again switched through.

XIII. Release of a toll connection When the called subscriber has cleared, the speech lines are disconnected by de-energisation of the relays G and TR as described under the foregoing sub-headingX. To release the connection, the'to-ll operator opens the circuit for the relay C (Figure 1) in the known manner. For the duration of the .delay in release of the relay A, a long A. C. impulse is sent through the line- VL in the repeater Ue2, the relays CR and E (Figure 2) are de-energised and the circuit for the line VL is opened so as to cause the connector LW to be cleared (as described under the foregoing sub-heading V. If the connection is made through a number of exchanges and a number of lines, the release of the devices such as the relays G and R which serve to switch through the speech lines may be effected simultaneously in all repeaters on receipt of one current impulse cornbination. If, on the other hand, those devices are to be released stage by stage,` from exchange to exchange, then different current impulse combinations must be transmitted successively through the various lines. f

The devices for the transmission and the reception of such current impulse combinations may be constructed in any desired manner. Synchronously running distributors may also be employed such as are known in telegraph arrangements. In this way, combinations of a number of current impulses of equal length or of current pauses may be transmitted and be distributed by the rotary distributor to appropriate receiving devices which evaluate them by means of pyramidally arranged contacts.

I claim:

1. A telephone installation comprising a plurality of exchanges, trunk lines between said exchanges, repeaters inductively connected to the ends of said trunk lines, at least one calling subscribers line, at least one called subscribers line, a speech circuit in each of said repeaters, switch means associated with said repeaters'means operated as a consequence of said called subscriber replying for making said. switch means operative to switch in said speech circuits and means operated as a consequence of one of said subscribers replacing his receiverfor making said switch means operative to disconnect said speech circuits. l

, 2. A telephone'installation according to claim 1, comprising also devices associated with said repeaters for the transmission' of alternating current audible frequency impulses, devices associated with said repeaters for the reception. of

said alternating'current impulses, switch means 75 Vil 4ends of said trunk lines, at least vone ycalling-and one called`subscribers line,A a speech circuit in each of said repeaters, said speechci'r'cuit comprising af point of interruption, switch means associated with said repeaters for switching in said speech circuit, means made operative on removal of said called subscribers receiver for making vsaid switch means operative to switch in said repeaters `and adapted to' be madeinoperative by said switching in switch means.

4. A telephone installation comprising a plurality of exchanges, trunk lines between said exchanges, inductively connectedre'peaters at the lends of said trunk lines, at least one calling subscribersline and one called subscribers line, each of said repeaters comprising ra yspeech circuit including a point of'interruption, devicesr adapted to allow the passage of signal currents bridging said points of interruption, switch-11nea`ns associated with said repeaters for-switching in said speech circuits, means madeoperative when said called subscriber removes his receiver for making saidswitch means operative to switch in said speech circuits andmeans made operative when one of said subscribers replaces his receiver for making said switch means operative to disconnect said speech circuits.y

5. A telephone installation comprising a plurality of exchanges, trunk lines between said exchanges, inductively connected repeaters at the ends of said trunk lines, at least one calling sub'- scriber connected to a calling exchange, at least one called subscriber connected to a called exchange, switch devices associated with said calling exchange for the emission of signal currents to said calling subscriber, switch devices associated With said called exchange for the transmissionl of backward signals, said switch devices associated with the calling exchange being operated by said backward signals, switch means in each of said repeaters for the emission of current impulses and switch means in each of said repeaters for the reception of current impulses, a speech circuit having points of interruption in each yof said repeaters and switch means in each of said repeaters for switching in said speech circuit, means operated when said called subscribers receiver is removed for making said switch means operative toswitch in said speech circuits and means operated on replacement of the receiver of one of said subscribers for making said switch means operative to disconnect said speech circuits.

6. A telephone system comprising a plurality of exchanges, a plurality of subscribers lines connected to said exchanges, trunk lines connecting said exchanges, `repeaters arranged at the two ends of each oisaid trunk lines, speech lines in said exchanges connected to said repeaters, the connection in said repeaters of said speech lines and'saidY trunk lines being Vnormally open, switch means in said repeaters automatically operated when-a called subscriber replies for connecting a speech line to a trunk line and means for maintaining said connection only while talking conditions subsist.

'7. Avtelephone system comprising in combination at least one calling exchange having a speech line, a calling subscriber connected to said calling` exchange, at least one called exchange having connecting devices and a speech line, a called subscriber connected to said called exchange, at least oneftrunk line connecting said exchanges, repeaters arranged at the two ends of said trunk line, automaticv switches associated with said connecting devices and differently operated when said called subscriber replies and when he hangs up his receiver, each of said repeaters comprising normally open switch means between the trunk line and the associated speech line, means controlled by said automatic switches when the called subscriber replies for actuating said switch means so as to close the connection of said trunk Iline to said speech line and means for maintain.- ing said connection only while talking conditions subsist, Y' v 8. A telephone system comprising in combinationat least one calling exchange having a speech line, a calling subscriber connected to said calling exchange, at least one called exchange having connecting devices and a speech line, a called subscriber connected to said called exchange, at least one trunk line connecting said exchanges, repeaters arranged at the two ends of said trunk line,v each repeater comprising an alternating 'current receiving relay connected to said trunk line, means for transmitting alternating current impulses over saidtrunk line, circuits controlled by lsaidalternating current receiving relay, normally open switch means between said trunk line and the associated speech line, a relay for closing said switch means only when the called subscriber replies and means controlled by said relay for making said circuits controlled by said alternating current receiving relay ineffective.

9. A telephone system comprising in combination at least one calling exchange having a speech line, a calling subscriber connected to said calling exchange, at least one called exchange having connecting devices and a speech line, a called subscriber co-nnected to said called exchange, at least one trunk line connecting said exchanges, repeaters arranged at the two ends of said trunk line, each repeater comprising a receiving relay connected to said trunk line, means for transmitting impulses over said trunk line, normally open switch means arranged between said trunk line and the associated speech line, a relay for closing said switch means only when the called subscriber replies, a switching device operable only on receipt of a predetermined train of impulses and means controlled by said lastmentioned relay for controlling said switching device by said receiving relay.

10. A telephone system comprising in combination at least one calling exchange having a speech line, a calling subscriber connected to said calling exchange, at least one called exchange having connecting devices and a speech trunk line and the associated speech line, a 75 relay actuated on reply by the called subscriber for closing said switch means, a locking circuit for said closing relay, a receiving relay connected to said trunk line, a switching device operable only on the receipt of a predetermined trainof impulses and switched in by said closing relay so as tobe operated by said receiving relay and means actuated by said switching device for interrupting said locking circuit.

1l. A telephone system comprising in combination at least o-ne calling exchange having a speech line, a calling subscriber connected to said calling exchange, at least one called eX- change having connecting devices and a speech line, a called subscriber connected to said called exchange, at least one trunk line connecting said exchanges, repeaters arranged at the two ends of said trunk line, speech ampliers arranged at the ends of said trunk line, each repeater comprising norm-ally open switch means situated between thev trunk line and the associated speech line, a relay actuated on reply by the called subscriber for closing said switch means, means controlled by said relay for switching said amplifiers into action, means effective only while talking conditions subsist between the calling and the called subscribers for holding said closing relay energised.-

12. A telephone system comprising in co-mbination at least one calling exchange having a speech line, a calling subscriber connected to said calling exchange, at least one called exchange having connecting devices and a speech line, a called subscriber connected tosaid called exchange, at least one trunk line connecting said exchanges, repeaters arranged at the two ends of said trunk line, each repeater comprising normally open switch means situated between said trunk line and theassociated speech line, a relay actuated on reply by the called subscriber receiving relay and an impulse emitting device for emitting a predetermined train of impulses prepared by said closing relay on its actuation.

13. A telephone system as claimed in claim l2, in which said repeater at the incoming end of the trunk line comprises also means actuated on the replacement of the called subscriber for switching said impulse emitting device into action.

14. A telephone system as claimed in claim l2, in which said repeater at the outgoing end of the trunk line comprises also means connected to the speech line of the calling exchange and actuated by a control current received over said sp-eech line when talking conditions exist between said subscribers for switching said impulse emitting means into action. f

l5. A telephone installation comprising a plurality of exchanges, trunk lines between said exchanges, repeaters inductively connected tothe ends of said trunk lines, at least one calling subscribers line, at least one called subscribers line, speech amplifying means associated with said repeaters, a speech circuit in each of said repeaters, switch means associated with said repeaters, means operated on said called subscriber removing his receiver for making said switch means operative to switch in said speech circuitsand said speech amplifying means and means operated when one of said two subscribers replaces his receiver for making said switch means operative to disconnectl said speech circuits and said speech amplifying means.

. MARTIN HEBEL. 

